almost sounds to me like a steer angle sensor problem.
if the steer angle sensor has an issue it cuts the drive back to a creep speed and normally displays an A on the dash display.
it could still have some type of problem with the LED's on the board but not detect an error.
this would be one of the first things i'd check after ruling out the directional contact tips, motor cables and motors themselves.

If this problem is relating to the other thread you started about the code FL? the FL is displayed when there is a fault in the drives.
If there is a short circuit in the drives, the logics will deactivate the line contactor and the contactor tips will open. The microprocessor looks for the difference between right and left side failure. Emitter wire 37 for the right side transistor emitter and the wire 41 for the left emitter.
If the voltage on either emitter is high when it should be low the fault code is displayed.
- Fr for right emitter, wire 37 high
- FL for left emitter, wire 41, high
- F for both right and left emitters, wire 37 and 41 high

now since you have recently replaced the drive transistors i would still take a look at the steer angle board since it is directly inline with the motor control and determines the speed of either mother depending on the angle of the steer wheel. The left side could be shorted and causing the imbalance in motor control.

think is better to start checking motors, before strip parts appart.
it is possible that transistor/drive card could have been damaged again if have a short in motor or their power cables.
you may want to check:
1-motor terminals against its frame for shorts, brushes beeing seated in good shape on conmutator. motor cables against frame
have found cables rubbing on hoses (steel recovering) doing short circuit.
also check the big resistors(R312,R302) for a good terminal
contact.
If contactors come in, they are making contact (not losing voltage through their tips)

roldann, dont regognise it as ev100, ( read post couple of days ago cat ep15t ), motor lhs turns very slow cuts out when steering turned , rhs no drive have replaced small card and both transistor packs, it is possible card might have been damaged again before i replaced transistors , contactors come in ok have not stripped yet, have no fault code ? thanks

hi, trev.
by your description it is the FBS15 using the TR2000 control panel/microcommand sysytem(the other option is EV100 lx).
What is the problem with your truck?